The invention relates to a screen-printing device for printing a substrate, comprising at least one printing station having a removable stencil, a printing-medium feed and a squeegee device, a cleaning unit which can be displaced to and fro in said stencil at least in a longitudinal direction, feed means for feeding cleaning liquid into said stencil, and discharge means for removing printing medium and/or cleaning liquid from said stencil.
A screen-printing device of this nature is known from NL-C-1005308, which, in FIG. 6, shows a printing station of the device, having a removable stencil and a squeegee device arranged therein. The top side of the squeegee device forms a guide face over which a cleaning unit can be moved to and fro. The cleaning unit is provided with a plurality of spray heads which are directed at the stencil and at the squeegee device. The spray heads are intended to deliver a cleaning liquid during a cleaning operation. The cleaning liquid which is delivered removes the printing medium from the squeegee device and from the inside of the stencil, mixes with the residual printing medium and collects in the bottom of the stencil. The squeegee device is designed with integral discharge means which comprise a discharge channel extending over the entire length in the squeegee device and provided with a plurality of suction openings which lie next to one another and open out in the bottom of the stencil. During the cleaning operation, the discharge channel is connected to a suction installation, and the cleaning liquid, together with the residual printing medium, is sucked out of the bottom of the stencil.
A drawback of this known screen-printing device is that the discharge means do not always function as desired. The suction force varies for each suction opening. The discharge channel has to be connected to a relatively powerful suction installation in order for an adequate suction result to be obtained over the entire length of the stencil. One or more suction openings becoming blocked is a regular occurrence. To rectify this problem, the entire squeegee device has to be removed from the stencil. Another problem which is regularly encountered is that false air is already being sucked in at one of the suction openings, while liquids which are to be sucked out are still located in the area of the other suction openings. The squeegee device with integral discharge means is relatively expensive and complex to produce, and is relatively heavy and consequently difficult to handle.
The object of the present invention is to provide a screen-printing device in which these drawbacks are eliminated.
According to the invention, this object is achieved by means of a screen-printing device according to claim 1. The screen-printing device comprises one or more printing stations, each having a removable stencil and a squeegee device extending inside it. The screen-printing device comprises feed means for feeding cleaning liquid into the stencil, and discharge means for removing residual printing medium and/or cleaning liquid from the stencil. The discharge means are provided on a displaceable cleaning unit which can be moved to and fro in the longitudinal direction inside the stencil, and comprise a suction nozzle which can be connected to a suction installation. The cleaning unit advantageously enables the stencil to be gradually sucked empty in a very thorough and efficient way from the left to the right and vice versa. During a cleaning operation, cleaning liquid is fed to the stencil, and the cleaning unit, with the suction nozzle operating, is moved to and fro one or more times through the stencil. In the process, the entire capacity of the suction installation is converted in concentrated form into a strong suction force which is always acting on a relatively small part of the bottom of the stencil. There will be virtually no more blockages in the discharge means, and any such blockages can easily be repaired outside the stencil, without the entire squeegee device having to be removed from the stencil for this purpose. The squeegee device may be of more lightweight, less complex and less expensive design. This is advantageous in particular because it is often the case that a plurality of squeegee devices are used for each printing station. Sucking in false air no longer has an adverse effect on the suction results, but rather can in fact be used as an indicator that the cleaning unit should be displaced to the next part of the bottom.